A silicon nitride sintered body is an example of a ceramic for structural materials and is applied to a bearing, an automotive glow plug and the like. In recent years, other than a sintered body, for example, an α-type silicon nitride powder having a controlled particle morphology is applied to a filler and the like of various materials and it's becoming widely used. Also, a high-purity α-type silicon nitride powder is utilized as a raw material of an oxynitride or nitride phosphor. For example, in Japanese Unexamined Patent Publication (Kokai) No. 2002-363554, a yellow a sialon phosphor is disclosed. The a sialon is a phosphor larger in the amount of a red component than Y3Al5O12:Ce3+ (YAG) that is used as a yellow phosphor in conventional white light-emitting diodes and therefore, a warm white color can be obtained. For this reason, the above sialon phosphor is expected to become more widely used as a phosphor for future illumination.